Preparation of YAG gel coated ZrB2–SiC composite prepared by gelcasting and pressureless sintering

In this paper, gelcasting and pressureless sintering of YAG gel coated ZrB₂–SiC (YZS) composite were conducted. YAG gel coated ZrB₂–SiC (YZS) suspension was firstly prepared through sol–gel route. Poly (acrylic acid) was used as dispersant. YZS suspension had the lowest viscosity when using 0.6 wt.% PAA as dispersant. Gelcasting was conducted based on AM–MBAM system. The gelcast YZS sample was then pressureless sintered to about 97% density. During sintering, YAG promoted the densification process from solid state sintering to liquid phase sintering. The average grain sizes of ZrB₂ and SiC in the YZS composite were 3.8 and 1.3 μm, respectively. The flexural strength, fracture toughness and microhardness were 375 ± 37 MPa, 4.13 ± 0.45 MPa m^1/2 and 14.1 ± 0.5 GPa, respectively.     

Modelling of carbon–carbon composite manufacturing processes

This paper is devoted to the modelling of technological processes of manufacturing of siliconized carbon–carbon composites. The developed model describes the changes that occur in the properties of the composites (strength, elastic moduli, shrinkage) during the technological cycle of manufacturing and also the residual stresses generated in composite structures. It is shown that the level of the residual stresses and the character of changes in the properties of carbon–carbon composites essentially differ from those of polymer–matrix composites.     

The effect of size of the SiC inclusions in the AlN–SiC composite structure on its electrophysical properties

AlN–SiC–Y₃Al₅O₁₂ composite materials with a high absorption of microwave frequency (27–65 dB/cm) produced by pressureless sintering of mixtures consisting of AlN(2H), Y₂O₃, and SiC (6H) in 46, 4, 50 wt %, respectively, have been studied. The SiC components of the mixtures were used in sizes of 1, 5, and 50 μm. It has been shown that the resistivity of the developed materials depends essentially on the materials structures: sizes of SiC inclusions, distances between them, and state of the interfaces. It has been found that the increase of the SiC inclusions sizes in the material structure from 3 to 7 μm results in the decrease of the resistivity from 10⁴ to 90 Ω·m, and at the decrease of the SiC inclusions sizes from 3 to 0.5 μm there forms a SiC uninterrupted skeleton, which also decreases the resistivity to 210 Ω·m. Thus, composite materials that contain 50 wt % SiC (inclusions sizes of 3 μm) are the most efficient in producing absorbers of microwave radiation. Interlayers of yttrium aluminum garnet, which are located at the SiC grains boundaries, prevent the forming of AlN(2H)–SiC(6H) solid solutions and thus, make it possible to keep high dielectric characteristics of a composite material based on aluminum nitride and afford a high absorption of a microwave radiation.     

Properties of carbon nano-tubes–Cf/SiC composite by precursor infiltration and pyrolysis process

Carbon nanotubes (CNTs) were introduced into the precursor infiltration and pyrolysis (PIP) carbon fiber reinforced silicon carbide matrix (C_f/SiC) composite via the infiltration slurry. The weight fraction of CNTs in the composite was 0.765‰. The fiber–matrix interface coating was prepared through chemical vapor deposition (CVD) process using methyltrichlorosilane (MTS). Effects of the CNTs on mechanical and thermal properties of the composite were evaluated by three-point bending test, single-edge notched beam (SENB) test, and laser flash method. Attributed to the introduction of the small quantity of CNTs, flexural strength and fracture toughness of the C_f/SiC composite both increased by 25%, and thermal conductivity at room temperature increased by 30%.     

The preparation and mechanical properties of carbon–carbon/lithium–aluminum–silicate composite joints

Silica carbide modified carbon cloth laminated C–C composites have been successfully joined to lithium–aluminum–silicate (LAS) glass–ceramics using magnesium–aluminum–silicate (MAS) glass–ceramics as interlayer by vacuum hot-press technique. The microstructure, mechanical properties and fracture mechanism of C–C/LAS composite joints were investigated. SiC coating modified the wettability between C–C composites and LAS glass–ceramics. Three continuous and homogenous interfaces (i.e. C–C/SiC, SiC/MAS and MAS/LAS) were formed by element interdiffusions and chemical reactions, which lead to a smooth transition from C–C composites to LAS glass–ceramics. The C–C/LAS joints have superior flexural property with a quasi-ductile behavior. The average flexural strength of C–C/LAS joints can be up to 140.26 MPa and 160.02 MPa at 25 °C and 800 °C, respectively. The average shear strength of C–C/LAS joints achieves 21.01 MPa and the joints are apt to fracture along the SiC/MAS interface. The high retention of mechanical properties at 800 °C makes the joints to be potentially used in a broad temperature range as structural components.     

The ballistic performance of SiC–AA7075 functionally graded composite produced by powder metallurgy

The potential of silicon carbide reinforced Functionally Gradient Material (FGM) to be used as armor material was investigated under the impact of armor piercing projectile. For this purpose, the SiC–Aluminum Alloy (AA) 7075 functionally graded composite at different thicknesses was produced from the metallic and ceramic powders via powder metallurgy method. Before the ballistic testing, the precipitation hardening behavior of the samples was determined. And also, the microstructural characterizations of the samples were done with the aid of microscopy techniques. Next, the FGM samples were tested using armor piercing projectile to analyze their impact behavior. In the produced samples, some pore formation was detected. The ballistic experiments showed that the investigated FGMs (up to a thickness of 25 mm) did not withstand the impact of the projectile. At the tested samples, some major cracks and plug formation were detected at macrolevel while there were some microcracks, deformed and elongated grains in the regions near to the deformation zone of the samples.     

Effects of SiC coating on ablation resistance of carbon fibre reinforced BN–Si3N4 matrix composite

Abstract

A SiC coating was prepared on the surface of a carbon fibre reinforced BN–Si₃N₄ composite by chemical vapour deposition. The coating was characterised by SEM and XRD, and the ablation behaviours of the coated and uncoated composites were investigated and compared. The coating is mainly amorphous SiC and quite compact; the ablated area of the composite is reduced considerably by the coating and the coated composite presents a lower linear ablation rate of 21˙4% and a lower mass ablation rate of 51˙6%. The SiC coating covers over the pores on the surface of the ablative composite, which prevents the flame from spreading to other regions and from penetrating the inside of the composite. As a result, both the chemical erosion and the mechanical denudation are restrained and the ablation resistance of the composite is improved.     

Simulated strength and structure of carbon–carbon reinforced composite

The atomistic simulations of carbon nanotube (CNT) – carbon reinforced composite material are reported. The studied composite samples are obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into a pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for the CNT–reinforced composites, since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, CNTs are able to increase the critical component of its initially highly anisotropic Young modulus by 2–8 times. The linear thermal expansion coefficients do not exceed 10⁻⁶ to 10⁻⁵ K⁻¹, making this material applicable for novel aviation and space vehicles. The degree of dispersion of CNTs within graphite matrix is found to drastically influence composite properties.     

Failure behavior investigation of a unidirectional carbon–carbon composite

The failure behavior and morphology of a carbon–carbon composite (C–C composite) manufactured by isothermal chemical vapor infiltration was studied by three-point bending tests, polarized light microscope and scanning electron microscope, respectively. The C–C composite was reinforced by PAN-based carbon fiber aligned in only one direction. Flexural strength and modulus of the composite were 200.9 MPa and 50.5 GPa, respectively. Failure behavior of the unidirectional C–C composite can be described as three stages including brittle fracture behavior at beginning, quasi-ductile behavior finally, and fluctuation behavior between them. Two main kinds of cracks, namely cracks parallel and perpendicular to loading direction alternately resulted in deformation evolution of the composite. The strength of interfacial bonding and cracks orientation played key roles to failure behavior of C–C composite.     

Modelling of carbon–carbon composite ablation in rocket nozzles

The modelling of ablation of carbon/carbon (C/C) composites utilized as rocket engine hot parts is addressed under the angle of the competition between bulk transport of reactants and heterogeneous mass transfer, associated to reactivity contrasts between constituent phases. A numerical solver based on a simple model and built on a VOF technique allows direct simulation at two scales. Its application to actual complex materials is performed; the results are consistent with experimental data and help understanding the origin of the material behaviour, either in terms of acquired surface morphology or in terms of effective recession rate.     

Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles–polymer composite films

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles–polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980 °C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of ～18.6 dB in 26.5–40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction.     

Effect of titanium on copper–titanium/carbon nanofibre composite materials

Copper/carbon nanofibre composites containing titanium varying from 0.3 wt.% to 5 wt.% were made, and their thermal conductivities measured using the laser flash technique. The measured thermal conductivities were much lower than predicted. The difference between measured and predicted values has often been attributed to limited heat flow across the interface. A study has been made of the composite microstructure using X-ray diffraction, transmission electron microscopy and Raman spectroscopy. It is shown in these materials, that the low composite thermal conductivity arises primarily because the highly graphitic carbon nanofibre structure transforms into amorphous carbon during the fabrication process.     

Fabrication of an aluminum–carbon nanotube metal matrix composite by accumulative roll-bonding

Accumulative roll-bonding was adapted to fabricate a carbon nanotube (CNT)-reinforced aluminum matrix composite. Its microstructure was investigated by transmission electron microscopy, and it was confirmed that the nanotubes were embedded into the metal matrix while maintaining their multiwalled structure. Measurements revealed that the as-received CNTs had a bimodal diameter size distribution, while only nanotubes with diameters >30 nm and >30 walls were retained during four consecutive rolling operations at 50% reduction.     

Electrocatalytical oxidation and sensitive determination of acetaminophen on glassy carbon electrode modified with graphene–chitosan composite

The electrochemical behaviors of acetaminophen (ACOP) on a graphene–chitosan (GR–CS) nanocomposite modified glassy carbon electrode (GCE) were investigated by cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Electrochemical characterization showed that the GR–CS nanocomposite had excellent electrocatalytic activity and surface area effect. As compared with bare GCE, the redox signal of ACOP on GR–CS/GCE was greatly enhanced. The values of electron transfer rate constant (k_s), diffusion coefficient (D) and the surface adsorption amount (Γ^?) of ACOP on GR–CS/GCE were determined to be 0.25 s^? 1, 3.61 × 10^? 5 cm² s^? 1 and 1.09 × 10^? 9 mol cm^? 2, respectively. Additionally, a 2e^?/2H⁺ electrochemical reaction mechanism of ACOP was deduced based on the acidity experiment. Under the optimized conditions, the ACOP could be quantified in the range from 1.0 × 10^? 6 to 1.0 × 10^? 4 M with a low detection limit of 3.0 × 10^? 7 M based on 3S/N. The interference and recovery experiments further showed that the proposed method is acceptable for the determination of ACOP in real pharmaceutical preparations.     

Computational analysis of the thermal conductivity of the carbon–carbon composite materials

Experimental data for carbon–carbon constituent materials are combined with a three-dimensional stationary heat-transfer finite element analysis to compute the average transverse and longitudinal thermal conductivities in carbon–carbon composites. Particular attention is given in elucidating the roles of various micro-structural defects such as de-bonded fiber/matrix interfaces, cracks and voids on thermal conductivity in these materials. In addition, the effect of the fiber precursor material is explored by analyzing PAN-based and pitch-based carbon fibers, both in the same type pitch-based carbon matrix. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibers and (b) a macro scale comparable with the thickness of carbon–carbon composite structures used in the thermal protection systems for space vehicles. The results obtain at room temperature are quite consistent with their experimental counterparts. At high temperatures, the model predicts that the contributions of gas-phase conduction and radiation within the micro-structural defects can significantly increase the transverse thermal conductivity of the carbon–carbon composites.     

Process and mechanical properties of carbon/carbon–silicon carbide composite reinforced with carbon nanotubes grown in situ

A hierarchical C_f/C–SiC composite was fabricated via in situ growth of carbon nanotubes (CNTs) on fiber cloths following polymer impregnation and pyrolysis process. The effects of CNTs grown in situ on mechanical properties of the composite, such as flexural strength, fracture toughness, crack propagation behavior and interfacial bonding strength, were evaluated. Fiber push-out test showed that the interfacial bonding strength between fiber and matrix was enhanced by CNTs grown in situ. The propagation of cracks into and in fiber bundles was impeded, which results in decreased crack density and a “pull-out of fiber bundle” failure mode. The flexural strength was increased while the fracture toughness was not improved significantly due to the decreased crack density and few interfacial debonding between fiber and matrix, although the local toughness can be improved by the pull-out of CNTs.     

Effect of environment atmosphere on thermal shock resistance of the ZrB2–SiC–graphite composite

The thermal shock resistance of the ZrB₂–SiC–graphite composite was evaluated by measuring the retention of the flexural strength after the electrical resistance heating to the temperature ranging from 1000 °C up to 2500 °C. The experiment was operated in two different environment atmospheres (pure oxygen and low oxygen partial pressure which mixed O₂ and Ar with 1:9) at total pressure 2000 Pa. The residual strength for the specimen decreased gradually as the temperature increased up to 2200 °C, and it was slightly higher when heated in low oxygen partial pressure environment than in pure oxygen. In contrast to the specimen heated in low oxygen partial pressure environment, the residual strength for the specimen in pure oxygen increased steeply as the temperature increased from 1600 °C up to 1800 °C. The analysis of the SEM observations combined with EDS confirmed that the surface oxidation played a positive role in the thermal shock resistance of the ZrB₂–SiC–graphite composite with different environment atmospheres. The results here pointed out a potential method for charactering the effect of environment atmosphere on thermal shock resistance of the ZrB₂–SiC–graphite composite.     

Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.